Method for producing a rigid structure based on curved metal tubes for forming a rear cantilever seat

ABSTRACT

The invention relates to a method for producing a rigid structure ( 5 ) based on curved metal tubes for forming a seat ( 1 ) of the rear cantilever type such as a chair or an armchair, characterized in that it comprises at least the steps involving forming two elongated one-piece lateral elements ( 10 ) by bending, each element at least being formed by a first base tubular portion ( 11 ) extending forwards, at a first bottom front bending zone ( 12 ), by a first front tube ( 13 ) erected upright and extending rearwards, at a first top front bending zone ( 14 ), by a lateral seating tube ( 15 ), said tubes used during bending by said method being made of a high carbon content, preferably between approximately 0.85 and 2.1%, steel alloy and the bending operations being performed cold before any type of subsequent heat treatment for hardening the steel that is used.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a method of producing a rigid structure fromcurved metal tubes to form a seat of the cantilevered type, such as achair or armchair.

PRIOR ART

Producing chairs or armchairs with a rear cantilever, i.e., with a seatthat “floats” above the ground because of the absence of vertical rearlegs is known. These seats have a particularly, aesthetic shape, with acomfortable and much appreciated “airy” structure.

Typically, these seats are made by bending hollow metal tubes with anexternal diameter of 20 or 30 mm and a material thickness of betweenapproximately 2 and 3 mm, so that the tube, which is suspended in thehollow at the level of the seat, does not bend under the weight of theperson who sits on the seat.

However, these seats are often massive/heavy because of the diameter ofthe tubes and the possibilities of different designs are quite limited.Indeed, because of the bending angles used, which are necessarilyproportional to the diameters of the tubes used, the models all look thesame, at least in terms of the legs and the general structure thatresults therefrom.

Furthermore, with respect to the processing technique used in the priorart, in order for a solid or hollow metal tube to be bendable, it mustbe made of a relatively ductile material For example, as a rule, for ahydraulic type tube (e.g., a gas pipe) made of low-alloyed basic steelwith a low carbon content (on the order of 0.18%), this tube should havean external diameter of approximately 25 mm. Below this value, it bendstoo much to be stable, and it may even break under the weight of theuser (due to the defects in its properties, i.e., it is ductile to bebendable, with the consequences that this implies for its mechanicalstrength).

Cold bending normally makes it possible to produce large quantities ofidentical parts with constant mechanical characteristics. With hotbending, this is not possible because the temperature rise alters theintrinsic mechanical characteristics of the steel. Moreover, as heatingof the same piece and/or of one identical to another is hardlyhomogeneous, the bending radii are never exactly the same so that aprocess of this type is hardly industrial but rather reserved forimplementation of a craft technique.

High-alloy steels, on the other hand, offer greater hardness after heattreatment, but they are not bendable at this level of hardness.

Finally, variants with solid and flat bars exist, for example those thatare 40 mm wide and 15 mm high, but the resulting seats remain massiveand quite similar in design.

Prior art processes for manufacturing this type of seat are thereforenot optimized and do not allow, in particular, the creation of thintubular structures, for example, those close to 15 mm in diameter, witha high resistance to bending and breaking to avoid breaking whileremaining comfortable.

[00.10] The purpose of the invention is to remedy this problem and to beable to manufacture a cantilevered (rear) chair with thinner tubediameters (15 mm) than those used in previous technology (20-30 mm). Forthis purpose, it proposes to cold curve the lateral parts of the seatstructure supporting the user's weight, i.e., tubes made of a steel witha high carbon alloy but in the annealed state (softened) in order to becold bendable, and then to carry out a heat treatment of the curvedstructure thus obtained in order to obtain maximum hardness, so as toproduce a thinner but highly mechanically-resistant part that keeps theseat from bending under the weight of the person sitting on the seat.

DISCLOSURE OF THE INVENTION

The present invention seeks to remedy these disadvantages with acompletely novel approach.

To this end, according to a first aspect, this invention relates to amethod of producing a rigid structure based on curved metal tubes toform a seat of the rear cantilever type, such as a chair or an armchair,characterized in that it comprises at least the steps consisting offorming, by bending, two elongated one-piece lateral elements, eachconsisting of at least one primary tubular portion of the foot extendingtowards the front, at a first low frontal bending zone, by an uprightfront primary tube extending towards the rear, at a first high frontalbending zone, by a lateral seat tube, said tubes used during bending bysaid method being made of alloy steel and bending being carried outbefore any type of subsequent heat treatment for hardening the steelused.

Thus, the load-bearing structure of the seat is reinforced, without itappearing either too massive or too fragile, and with a particularlyhigh resistance to bending at the level of the overhang, supportingloads in excess of 120 kg without breaking or bending in an excessivelypronounced manner.

The invention is implemented according to the following embodiments andvariants set forth below, which are to be considered individually or inany technically operative combination:

-   -   the steps of bending the elongated lateral members are carried        out with steel tubes having a carbon content between        approximately 0.85 and 2.1%, preferably between approximately        1.15% and 2%;    -   the steps of bending the elongated lateral members are carried        out with solid tubes having a diameter of between approximately        10 and 25 mm, preferably between 15 and 20 mm;    -   the steps of bending the elongated lateral members, forward and        down and forward and up, are performed at approximately 90°,        with a median bending radius of approximately 1.5 to 3 times the        diameter of the tube used;    -   the steps of bending the elongated lateral members form a single        continuous arc at approximately 180° between the primary foot        tube portion and the seat tube.

Advantageously, the method consists of connecting the two one-pieceelongated lateral members to at least a third hollow tube structuralmember at the level of the primary tubular foot portion.

Preferably, the method consists of producing a third independentstructural element in the form of two secondary foot tube portions,connected respectively and in a parallel manner to the primary foot tubeportions and each extending, in a second lower frontal bending zone,into a front secondary tube erected upwardly parallel to the frontprimary tube, each front secondary tube extending, in a second upperfrontal bending zone, into a single front transverse tube delimiting theseat with the two lateral seat tubes.

This solution allows for the creation of a new style of cantileveredseat. The thinner diameter allows for different designs, especially withdoubled tubular legs forming a symmetrical paperclip type seat flat onthe floor instead of a U shape.

According to one particular embodiment, the process consists ofproviding the free ends of the solid tubes of the two lateral elementswith undercut nipples having a diameter identical to the internaldiameter of the hollow tubes of the third element, then inserting saidundercut nipples of the first two lateral portions into the hollow tubesof the second portion over a length of 1 to 2 cm before soldering orwelding the assembly to form the complete structure.

Preferably, the process consists of connecting the free ends of theprimary and secondary tubular portions of each foot by bending a. 180°arc between said tubes.

According to particular embodiments:

-   -   the method comprises a step consisting of securing the front        primary tubes and the front secondary tubes to each other by        means of at least one reinforcing crossbar,    -   the process consists of arranging said reinforcing bar at        raid-height of the front primary and secondary tubes;    -   the method comprises a step consisting of extending two of the        seat side tubes, at a first upper dorsal bending zone, by two        rear tubes also belonging to the seat structure;    -   the method further consists of bending the two rear tubes upward        at a second dorsal curving zone to form a backrest;    -   the method includes a subsequent step of attaching a rigid        openwork plate or mesh or frame, preferably metal, between the        cross tube, the seat side tubes and the seat back tubes; and.    -   the method includes a subsequent step of inserting a two-part        seatpad, a top part and a bottom part, sandwiching said        plate/mesh/frame so as to make it completely invisible from the        outside.

BRIEF DESCRIPTION OF THE FIGURES

Further advantages, purposes and characteristics of this invention areapparent from the following description made, for the purpose ofexplanation and not limitation, with reference to the attached drawings,in which:

FIG. 1 is an isometric perspective view of a seat according to thisinvention,

FIG. 2 is an isometric perspective view of the tubular structureconstituting the seat in FIG. 1,

FIG. 3 is a partial isometric and locally exploded view of FIG. 1,

FIG. 4 is a detailed view of FIG. 3,

FIG. 5 is an isometric perspective view of an embodiment of FIG. 1,

FIG. 6 is a side view of FIG. 5,

FIG. 7 is a perspective view of an alternative structure of FIGS. 1through 4 and 5 through 6,

FIG. 8 is a cross-sectional view of FIG. 7 illustrating the connectionbetween the different elements of the tubular structure,

FIG. 9 is another alternative embodiment of FIGS. 1 and 5, and

FIG. 10 depicts an alternative chair with an armrest.

DESCRIPTION OF THE EMBODIMENTS

FIGS. 1 to 4 represent a first embodiment of a chair 1 according to thisinvention.

This chair 1 has a rigid structure 5 based on tubes with an externaldiameter of 15 mm which are curved according to a well-known technologydescribed later. This technology may also be used for tubes of differentdiameters, preferably in the range of approximately 10 to 25 mm, andmore preferably between 15 and 20 mm.

Thus, this chair 1 comprises two first one-piece elongated side elements10 (in dark gray in FIG. 2) a third structural element 20 (in light grayin FIG. 2) and a fourth back element 30 (in light gray in FIG. 2).

Each first elongated one-piece lateral element 10, thus realized in theform of a continuous tube, comprises a primary tubular foot portion 11extending forward, at a first lower frontal bending zone 12, by a frontprimary tube 13 (or vertical post) erected upwardly and extendingrearward, at a first upper frontal bending zone 14, by a lateral primaryseat tube 15. This structure may also be seen in FIGS. 5 to 8.

As provided for in the invention, all the tubes of these first elongatedside members 10 are solid and made of steel with a higher carboncontent, preferably between approximately 0.85 and 2.1%, preferablybetween 1.15 and 2%, and the bending in zones 12 and 14 is carried outcold before any type of subsequent heat treatment for hardening thesteel is used.

The front bottom 12 and front top 14 bending steps of the elongated sideelements 10 are carried out at approximately 90°, preferably cold, on arigid frame known per se, with a median bending radius (along the axisof symmetry of the tubes) of approximately 1.5 to 3 times the diameterof the tube used.

According to this first embodiment shown in FIGS. 1 to 4, certain zonesof the structure 5 are “doubled”, or “paperclip-shaped”, which gives ita better grip on the ground on the one hand, and provides it with a veryoriginal aesthetic on the other hand.

Thus, a third internal element 20 of the structure 5 (light-colored inFIG. 2), made independently of the two elongated lateral elements 10,has two secondary tubular foot portions 21, connected respectively andin a parallel manner to the primary tubular foot portions 11 and eachextending in a second lower front zone 22 of bending at 90°, by a frontsecondary tube 23 erected upwards parallel to the front primary tube 13,each front secondary tube 23 being extended, in a second upper frontzone 24 of bending at 90°, by a single front transverse tube 25delimiting a seat structure 8 with the two lateral seat tubes 15.

The free ends of each foot are formed by a curve 26 forming a 180° arcbetween said parallel tubes of the secondary portions 21, giving thatparticular shape of a paperclip previously indicated. This allows the“sliders”, formed by the primary and secondary tubular portions 11 and21 and the curve 26 of each leg, to remain parallel to each other and tothe ground, while contributing to the rigidity of the structure 5 andproviding an aesthetically appealing appearance.

It should be noted that the third structure 30 has little or no effecton the weight-bearing capacity of the chair, since most of the weightrests on the two elongated solid tube side members 10, which are muchstronger.

Alternatively (not shown), it is possible to add transverse bars betweenthe primary 11 and secondary 21 tubular portions of each leg, atmid-length of the latter and/or close to the lower frontal bending zones12 and 22. In this case, the purpose of these bars is to maintainportions 11 and 21 of the feet parallel to each other.

Likewise, the front primary tubes 13 and the front secondary tubes 23are connected to each other by at least one reinforcing crossbar 28placed at mid-height and/or close to one and/or the other of the lowerfront bending zone 12 and the second upper front bending zone 24. Thisbar 28 allows a better stability between the 2 front tubes 13 and 23 ofthe vertical posts of the structure 5.

As may also be seen in FIGS. 1 through 4, a fourth structural member 30is provided on the back of the overall structure 5. More specifically,these are secondary lateral seat tubes 31 that are attached to theprimary lateral seat tubes 15 and that extend, at a first upper backzone 32 of bending at 90°, into two rear tubes 33 also belonging to theseat structure 8.

The two rear tubes 33 are then bent upwards at the level of a second 90°bent dorsal zone 34 to form a backrest 35 closed upwards by a 180° bendforming an inverted “U” and covered with a backrest lining 36 of a knowntype.

As illustrated in FIGS. 3 and 4, a rigid plate or mesh 40, preferablymetallic, is fixed (preferably by welding and/or brazing) between thefront transverse tube 25, the lateral seat tubes 15 and 31, and the rearseat tubes 33 together defining the seat structure 8.

A seat pad 50 is then incorporated into the seat structure 8.Preferably, this seat upholstery 50, made for example of leather orpadded imitation leather, consists of two independent parts 51 and 52.More precisely, the upper part 51 and the lower part 52 sandwich thesaid plate/mesh 40 in such a way as to make it completely invisible fromthe outside (see FIG. 1 for example). The front edge 50 a of each of theparts 51 and 52 is preferably flush with the front cross tube 25.

The upper part 51 of the seat upholstery 50 comprises front protrusions54 which are integrated between the tubes 13 and 15 on the one hand, andthe tubes 23 and 25 on the other hand, at the level of bends 14 and 24.

Similarly, the lower part 52 of the seat upholstery 50 has a rearhousing 53 that engages a rear protrusion 55 of the upper part 51 of theseat upholstery 50, as seen in FIG. 4. This allows the seat upholstery50 to be integrated as well as possible with the seat structure 8 of theoverall tubular structure 5. In particular, this type of assembly givesthe impression, at least from the front as well as from the sides, thatthe seat 50 forms a single element because the peripheral joining linesof the two parts 51 and 52 are actually hidden by tubes 25 and 15.

As contemplated by this invention, all of the tubes of the thirdstructural member 20 and the fourth dorsal member 30 have the sameoutside diameter as the tubes constituting the elongated side members10.

According to a variant of the embodiment illustrated by FIGS. 5 and 6and presenting a different aesthetic, the overall structure 5 isconstituted by only two long lateral elements 10 (in grey) identical tothose of FIGS. 1 to 4, i.e., composed of a continuous doubly bent tubecomprising a primary tubular portion of the foot 11 extending towardsthe front, at the level of a first lower frontal zone 12 of bending at90°, by a front primary tube 13 (or vertically upright) drawn upwardsand extending towards the rear, at the level of a first upper frontalzone of bending at 90° 14, by a lateral seat tube 15.

This chair 1 also comprises a third tubular structure 20 (light colored)“which closes the legs towards the rear” and which is constituted forthis purpose by two secondary tubular portions of legs 21 respectivelyextending the two primary tubular portions of legs 11, these twosecondary tabular portions of legs 21 being bent at 90° in lower rearbending zones 26 b in order to form a rear tube 29 disposedsubstantially in line with the backrest upholstery 36.

Similarly, the chair comprises a fourth tubular structure 30 (lightcolored) comprising two secondary lateral seat tubes 31 attached to theprimary lateral seat tubes 15, said secondary lateral seat tubes beingthis time bent upwardly at 90° in the upper dorsal bending zones 32 andare extended by rear tubes 35 b forming the support of the backrestupholstery 36.

FIGS. 7 and 8 illustrate the mode of connection of the elongated sideelements 10 made of solid tube (shaded tubes) with a third structuralelement 20 and a fourth dorsal element 30 according to an intermediatevariant (without a backrest structure) between FIGS. 1 to 4 (so-called“double slide” structure) and FIGS. 5 to 6, both of which are made ofhollow tube (light-colored tubes).

More specifically, as shown in the cross-section in FIG. 8, the upperand lower free ends 10 a of the solid (black colored) tubes of the twoelongated side members 10 are provided with undercut nipples 10 b havingan outer diameter D1 identical to the inner diameter D2 of the hollowtubes of the third (gray colored tubes) and fourth (light colored tubes)structural members 20 and 30.

To build the entire structure 5 of chair 1, it is sufficient to insertsaid undercut nipples 10 b of the two elongated side members 10 into thehollow tubes of the third structural member 20 and the fourth structuralmember 30 for a length of 1 to 2 cm before brazing or welding theassembly. This method of attachment is the same as that used for theoverall structures 5 of chair 1 in FIGS. 1 to 4 and 5 to 6.

The structure thus formed is therefore particularly thin, light, airy,and aesthetically pleasing, without compromising its strength andresistance to bending due to the design and shaping of the elongatedelements made of solid tubes cold curved in a soft state before thermalhardening in order to have a very high degree of hardness (63HRC).

The choice of steel used is also important. It is, as mentioned earlierin the description, a high carbon steel, typically approximately 1.15 to2%, so that it is rigid enough not to bend under the weight of the userbut also flexible enough to bend without breaking, while keeping apermanent and almost identical stability regardless of its weight.

Thus, a solid tube made of Z160 CDV12 (1.55% carbon), a steel known tobe brittle (steel for machine tools, sheet metal cutting tools, etc.)but in fact sufficiently elastic to provide a slight, comfortable springeffect (coax. 2-2.5 cm of bending range), might be chosen.

The solid tube of Z160 CDV12 in the annealed (soft) state is bentaccording to known techniques (on a rigid frame) with a median radius(at the transverse axis of the tube) of approximately 35 mm in bendingzones 12 and 14 for a tube with an outside diameter of 1.5 mm.

Hardening at a temperature above 900° C., e.g., 1000-1050° C., followedby tempering and then cooling, e.g., by cryogenics, are carried outafter bending in order to stiffen the resulting structure and achieve aservice hardness of approximately 63HRC.

In the embodiment shown in FIG. 9 the bending steps of the elongatedside members 10 form a single continuous 180° arc 12 (rather than twoindependent 90° arcs) between the primary foot tube portion 11 and theseat tube 15.

The same is true for bending arc 22 of the third structure 20 at thelevel of tubes 23 which follows the same curvature as tubes 13 of thefirst elongated side members 10.

Of course, only the primary foot tubular elements 11, the primary fronttubes 13 and the primary side seat tubes 15 are made of solid highcarbon steel tube.

The resulting chair 1 remains extremely stable and strong, with a designvery different from the two previous models, but retaining a solidtubular portion (part of the legs, of the front and of the seat) in theareas requiring increased resistance to flexing and breaking. Of coursethe structure 5 is similar to that of FIGS. 1 to 4, with the firstelongated side members 10 made of solid high carbon steel tube tosupport the weight and all the rest of the structure 5 (third and fourthstructural members 20 and 30) made of hollow tube.

FIG. 10 shows a chair 1 in which the elongated side elements 10 aresubstantially the same as in the previous embodiments (tube bent andthen heat-treated, bending 12 and 14 at approximately 90°), with thedifference that side tubes 15 no longer form a lateral part of the seatstructure 8 but an armrest 60. Likewise, the front transverse tube 25 ofthe third structure 20 no longer forms a front part of the seatstructure 8 but only serves to connect the lateral upright membersconstituted by front tubes 13 and 23. Each armrest 60 also has a sidetube 27 of the third structure 20 that is parallel to the side tube 15of each elongated member 10. The upholsteries of the seat 50 and thebackrest 36 form a single upholstery, for example, in the form of afabric or leather cloth stretched between the seat structure 8 and thefourth structural element 30. As in the previous variants, the user'sweight continues to be supported mainly by the lateral elongatedelements 10 which are more rigid than the rest of the structure.

It should be understood that the detailed description of thesubject-matter of the invention, which is given for illustrativepurposes only, does not in any way constitute a limitation, as thetechnical equivalents are also included within the scope of thisinvention.

Thus, the 180° angle or the 90° angles of the upper and lower frontbends may be slightly larger than these values, to give the seat aparticular shape with a slight tilt.

The legs of the seat are not necessarily parallel to each other but mayform a trapezoid.

The bending operations, in particular of the elongated side elements 10,may be performed under heat.

Steels other than the one mentioned might be considered, the principlebeing to find a steel that is cold bendable according to the desiredradius of curvature and that will have the same characteristics ofstiffness without breaking after hardening under the weight of theperson sitting on the chair.

The tubes may be hollow or solid, square, or rectangular incross-section, and the elongated side members 10 may be made with hollowtubes, preferably from 2 to 6 mm, for example with an internal diameterof approximately 5 mm. In this case, an intermediate sleeve-like partwill need to be provided instead of the nipples 10 b to connect theelongated side elements 10 to the third and fourth structural elements20 and 30.

The ends of the feet do not necessarily form a 180° arc but may assumemany other shapes.

The lattice or sheet 40 may be replaced by a simple frame connectedaround the inner perimeter of the seating structure 8 and covered, forexample, by a sheet of wood or other material to support the upholstery.

It is possible for the paperclip-like structure 5 to comprise not onlytwo parallel tubes, but three parallel tubes to form the legs and extendinto three front tubes, one of which forms the front post 25 of theseating structure 8, another forms the side posts 15 of the seatingstructure 8, and a last one is directed upwards to form armrests.

1. Method of producing a rigid structure based on metal tubes bent toform a seat of the rear cantilever type, such as a chair or an armchair,comprising the steps of: forming two one-piece elongated lateral membersby bending said metal tubes, each of the two one-piece elongated lateralmembers made of a primary tubular foot portion extending forwardly and,at a level of a first lower frontal bending zone, extending as a frontprimary tube erected upwardly and, at a level of a first upper frontalbending zone, extending rearwardly as a lateral seat tube, said metaltubes used during the bending by said method being made of steel, andcarrying out a subsequent heat treatment for hardening the steel afterbending said metal tubes.
 2. The method according to claim 1, whereinbending the metal tubes comprises bending the metal tubes which are madeof steel having a carbon content between about 0.85 and about 2.1%. 3.The method according to claim 1, wherein bending the metal tubescomprises bending solid tubes having a diameter between about 10 andabout 25 mm.
 4. The method according to claim 1, wherein bending themetal tubes comprises bending the metal tubes forward and down andforward and up at approximately 90°, with a median bending radius ofapproximately 1.5 to 3 times the diameter of the metal tubes used. 5.The method according to claim 1, wherein the step of forming the twoone-piece elongated lateral members by bending comprises forming asingle continuous arc of approximately 180° between the primary tubularfoot portion and the lateral seat tube.
 6. The method according to claim1, further comprising connecting the two one-piece elongated lateralmembers at the primary tubular foot portion of each of the two one-pieceelongated lateral members to a third structural element which is formedof a hollow tube.
 7. The method according to claim 6, further comprisingproducing the third independent structural element in the form of twosecondary tubular foot portions connected respectively and in a parallelmanner to the primary tubular foot portion of each of the two one-pieceelongated lateral members and each extending in a second lower frontbending zone into a front secondary tube erected upwards parallel to thefront primary tube, each front secondary tube extending in a secondupper front bending zone, into a single front transverse tube delimitinga seat structure with the two lateral seat tubes.
 8. The methodaccording to claim 7, further comprising providing the free ends of thesolid tubes of the two one-piece elongated lateral members with undercutnipples having an external diameter identical to an internal diameter ofthe hollow tubes of the third independent structural element, theninserting said undercut nipples of the two one-piece lateral membersinto the hollow tubes of the third element over a length of 1 to 2 cmbefore soldering or welding the assembly to form the structure.
 9. Themethod according to claim 8, further comprising forming, by bending, anarc of 180° at a free end of the primary tubular foot portion to connectthe free end of the primary tubular portion with a free end of thesecondary tubular portions.
 10. The method according to claim 6, furthercomprising securing the front primary tube and the front secondary tubeto each other with a reinforcing crossbar.
 11. The method according toclaim 10, further comprising arranging said reinforcing crossbar atmid-height of the front primary tube and the secondary tube.
 12. Themethod according to claim 6, further comprising connecting, in extensionof the lateral seat tubes, secondary lateral seat tubes, with rear tubesextending therefrom at a first high dorsal bending zone also belongingto the seat structure.
 13. The method according to claim 12, furthercomprising bending the two rear tubes upwardly at a second dorsalbending zone to form a backrest.
 14. The method according to claim 12,further comprising a subsequent step of attaching a rigid openwork plateor mesh or frame made of metal, between the front transverse tube, thelateral seat tubes, the secondary lateral seat tubes, and the rear seattubes.
 15. The method according to claim 14, further comprising asubsequent step of inserting a two-part seat pad, a top part and abottom part, sandwiching and thereby hiding from outside said plate,mesh, or frame.
 16. The method according to claim 2, wherein bending themetal tubes comprises bending the metal tubes which are made of steelhaving a carbon content between about 1.15% and about 2.0%.
 17. Themethod according to claim 3, wherein the bending the metal tubescomprises bending solid tubes having a diameter between about 15 mm andabout 20 mm.